Heat treating apparatuses having a magnetic drive system and related methods

Abstract

Embodiments of methods for vacuum heat treating refractory metal articles (e.g., implantable medical devices), and heat treating apparatuses for use in such methods are disclosed. Heat treating refractory metal articles under high vacuum (e.g., 10 −6 Torr) may improve strength and ductility and remove material contaminants (e.g., oxygen or hydrogen) that may be absorbed during manufacturing processes. Heat treating methods include disposing a refractory metal article in a heat treating apparatus, drawing a vacuum therein, and moving the article to a heated zone in the furnace using a drive system that permits movement of the article while the vacuum is maintained in the apparatus. A heat treating apparatus may include an elongate furnace tube that may be sealed and placed under vacuum, a heating element disposed around at least a portion of the tube, and a drive system configured for moving articles disposed inside the furnace tube while under vacuum.

What is claimed is: 
     
         1 . A heat treating apparatus for heat treating a refractory metal article, comprising:
 a guide tube defining a guide tube passageway;   a furnace tube fluidly coupled to the guide tube and defining a furnace-tube passageway in communication with the guide tube passageway;   a heating element disposed around at least a portion of the furnace tube, the heating element defining a heated zone in a first portion of the furnace tube having the heating element disposed therearound and the heating element defining an unheated zone in a second portion of the furnace tube outside the heating zone;   a guide rod structure including a proximal portion and a distal portion configured to support the refractory metal article; and   a magnetic drive system configured to move the guide rod structure axially within the guide tube passageway and the furnace-tube passageway to position the refractory metal article within the heated zone while a partial vacuum environment is maintained inside the guide tube and the furnace tube.   
     
     
         2 . The heat treating apparatus recited in  claim 1 , wherein the furnace tube is formed from a heat-resistant ceramic material. 
     
     
         3 . The heat treating apparatus recited in  claim 1 , wherein the heating element is configured to maintain a temperature in the heated zone in a range from about 800° C. to about 1500° C. 
     
     
         4 . The heat treating apparatus recited in  claim 1 , further comprising an interlock assembly connecting the guide tube and the furnace tube together, the interlock assembly being configured to permit a user to dispose the refractory metal article in the furnace tube. 
     
     
         5 . The heat treating apparatus recited in  claim 4 , wherein the interlock assembly includes a water-cooled jacket. 
     
     
         6 . The heat treating apparatus recited in  claim 4 , wherein the interlock assembly includes a bushing structure configured to guide the guide rod structure. 
     
     
         7 . The heat treating apparatus recited in  claim 1 , wherein the magnetic drive system includes:
 a magnetically responsive component coupled to the proximal end of the guide-rod structure, the magnetically responsive component being configured to fit inside the guide tube passageway of the guide tube; and   a magnetic actuator component disposed about a portion of the guide tube, the magnetic component being configured to magnetically interact with the magnetically responsive component through the guide tube to axially move the guide-rod structure in the guide tube passageway while the partial vacuum environment in the guide tube and the furnace tube is maintained.   
     
     
         8 . The heat treating apparatus recited in  claim 7 , wherein the magnetically responsive component further comprises a plurality of bearing elements disposed thereon between the magnetically responsive component and the inside of the guide tube. 
     
     
         9 . The heat treating apparatus recited in  claim 7 , wherein the magnetic actuator component includes:
 a collar disposed around a portion of the outside of the guide tube;   a plurality of depressions formed in the collar; and   a first plurality of magnets disposed in each of the plurality of depressions in the collar, the first plurality of magnets being configured to magnetically interact with the magnetically responsive component through the guide tube to permit movement of the guide-rod structure in the guide tube passageway and the furnace-tube passageway while the partial vacuum environment in the guide tube and the furnace tube is maintained.   
     
     
         10 . The heat treating apparatus recited in  claim 1 , further comprising:
 a vacuum pump coupled to the furnace tube and/or the guide tube; and   a vacuum sensor configured to detect and report a vacuum level in the furnace tube and the guide tube.   
     
     
         11 . The heat treating apparatus recited in  claim 10 , wherein the vacuum sensor and the heating element are operably coupled to a control system, the control system being configured to activate the heating element when a predetermined vacuum level is detected by the vacuum sensor. 
     
     
         12 . A method for heat treating a refractory metal article, the method comprising:
 disposing the refractory metal article in a heat treating apparatus, wherein the heat treating apparatus is configured for heat treating the refractory metal article in a vacuum environment so that chemical embrittlement does not occur in the refractory metal article before and/or during and/or after heat treating;   drawing a partial vacuum in the heat treating apparatus;   advancing the refractory metal article to a heated zone in the heat treating apparatus while maintaining the partial vacuum therein;   exposing the refractory metal article to a temperature in the heated zone for a period of time sufficient for modifying one or more of a mechanical or a chemical property of the refractory metal article; and   retracting the refractory metal article to an unheated zone in the heat treating apparatus while maintaining the partial vacuum therein.   
     
     
         13 . The method recited in  claim 12 , wherein modifying one or more of a mechanical or a chemical property includes at least one of:
 improving ductility of the refractory metal article; or   at least partially removing one or more chemical contaminants from the refractory metal article.   
     
     
         14 . The method recited in  claim 12 , wherein the refractory metal article is coldworked and/or includes a chemical contaminant selected from the group consisting of hydrogen, nitrogen, or oxygen at or above a threshold concentration sufficient to cause chemical embrittlement of the refractory metal article. 
     
     
         15 . The method recited in  claim 12 , wherein the refractory metal article includes a material selected from the group consisting of tantalum, niobium, tungsten, and alloys thereof. 
     
     
         16 . The method recited in  claim 15 , wherein the refractory metal article includes:
 about 75 to about 90 weight percent tantalum;   about 8 to about 12 weight percent niobium; and   about 2 to about 10 weight percent tungsten.   
     
     
         17 . The method recited in  claim 12 , wherein the heat treating apparatus includes:
 a guide tube defining a guide tube passageway;   a furnace tube fluidly coupled to the guide tube and defining a furnace-tube passageway in communication with the guide tube passageway; and   a heating element disposed around at least a portion of the furnace tube, the heating element defining the heated zone in a first portion of the furnace tube having the heating element disposed therearound and the heating element defining the unheated zone in a second portion of the furnace tube outside the heating element.   
     
     
         18 . The method recited in  claim 17 , further comprising:
 disposing the refractory metal article on a support structure disposed within the furnace tube passageway, wherein the support structure is operatively coupled to a magnetic drive system, the magnetic drive system including:
 an elongate guide rod structure having a proximal portion that includes a magnetically responsive component disposed thereon and a distal portion that includes the support structure coupled to the elongate guide rod; 
   sealing the furnace;   drawing the partial vacuum in the furnace;   advancing the refractory metal article into the heated zone by magnetically actuating the magnetically responsive component while a partial vacuum is maintained in the guide tube and the furnace tube;   exposing the refractory metal article to a selected temperature for a period of time sufficient to affect at least one of a chemical or mechanical property of the refractory metal article; and   retracting the refractory metal article to an unheated zone in the furnace tube after exposing the refractory metal article to the selected temperature by magnetically actuating the magnetically responsive component while a partial vacuum is maintained in the guide tube and the furnace tube.   
     
     
         19 . The method recited in  claim 14 , wherein the exposing includes heating the refractory metal article in the heated zone for a period of time in a range between about 30 seconds and about 2 hours. 
     
     
         20 . The method recited in  claim 19 , wherein the exposing includes heating the refractory metal article in the heated zone for a period of time in a range between about 10 minutes and about 20 minutes. 
     
     
         21 . The method recited in  claim 14 , wherein the exposing includes heating the refractory metal article in the heated zone at a temperature in a range between about 800° C. and about 1000° C. 
     
     
         22 . The method recited in  claim 21 , wherein the exposing includes heating the refractory metal article in the heated zone at a temperature in a range between about 1200° C. and about 1400° C. 
     
     
         23 . The method recited in  claim 14 , wherein the exposing includes heating the refractory metal article in the heated zone for a period of time in a range between about 10 minutes and about 20 minutes at a temperature in a range between about 1265° C. and about 1285° C. 
     
     
         24 . The method of  claim 14 , wherein drawing the partial vacuum includes drawing a vacuum in a range of about 25 Torr to about 10 −12  Torr in pressure. 
     
     
         25 . The method of  claim 14 , wherein drawing the partial vacuum includes drawing a vacuum in a range of about 10 −3  Torr to about 10 −7  Torr. 
     
     
         26 . A method for moving a refractory metal article in a vacuum environment, comprising:
 providing a heat treating apparatus configured for heat treating a refractory metal article under a partial vacuum, the heat treating apparatus including:
 a guide tube defining a guide tube passageway and a furnace tube defining a furnace tube passageway, the guide tube and the furnace tube being fluidly coupled and configured to contain a partial vacuum environment therein; 
 a heating element disposed around at least a portion of the furnace tube; and 
 a magnetic drive system disposed in the guide tube and the furnace tube; 
   disposing a refractory metal article within the heat treating apparatus on the magnetic drive system;   advancing the refractory metal article from a first portion of the heat treating apparatus to a second portion of the heat treating apparatus using the magnetic drive system while maintaining a partial vacuum therein; and   retracting the refractory metal article from the second portion of the heat treating apparatus to the first portion of the heat treating apparatus using the magnetic drive system while maintaining the partial vacuum therein.   
     
     
         27 . The method recited in  claim 26 , further comprising:
 advancing and/or retracting the magnetic drive system by magnetically actuating a magnetically responsive component of the magnetic drive system using a magnetic component disposed outside the guide tube,
 wherein the magnetic component is configured to magnetically engage with the magnetically responsive component through the guide tube in order to permit axial movement of the magnetic drive system in the guide tube passageway while maintaining the partial vacuum environment in the guide tube and/or the furnace tube. 
   
     
     
         28 . The method recited in  claim 26 , the magnetic drive system traversing a distance in a range of about 20 cm to about 200 cm while maintaining the partial vacuum environment in the guide tube and/or the furnace tube. 
     
     
         29 . The method recited in  claim 28 , the magnetic drive system traversing a distance in a range of about 50 cm to about 100 cm while maintaining the partial vacuum environment in the guide tube and/or the furnace tube.